As an electromagnetic clutch for use in an opening/closing apparatus for a vehicle door, there is known e.g. one having a worm gear, a worm wheel, an armature, a plate spring, a rotor, an electromagnetic coil, etc (see e.g. Patent Document 1).
With such electromagnetic clutch, at the time of non-powered state with no application of electric power to the electromagnetic coil, the armature and the rotor are either spaced apart from each other or in light contact with each other, so as to alleviate a force needed for a manual operation of the vehicle door. At the time of powered state with application of the electric power to the electromagnetic coil, the electromagnetic coil generates a magnetic force, which pulls the armature toward the rotor, so that the armature eventually comes into firm contact with the rotor. Under this condition, automatic opening/closing operations by motor drive become possible.
Further, with the electromagnetic clutch disclosed in Patent Document 1, a plate spring member is incorporated between the worm wheel and the armature. Fixing operations of the worm wheel, the plate spring member and the armature are done by mutual caulking via pins or fastening of screws. With this electromagnetic clutch, when no power is supplied to the electromagnetic coil, the plate spring member, with its resilient force, pulls the armature toward the worm wheel. As a result, there is formed a gap between the armature and the rotor, so that the electromagnetic clutch assumes a disengaged state. This is a condition of absence of direct coupling between the vehicle door and the motor. Accordingly, when the vehicle door is to be opened/closed by a manual operation, this manual operation can be done lightly. On the other hand, when power is supplied to the electromagnetic coil, the magnetic force generated from the electromagnetic coil pulls the armature into contact with the rotor, so that the electromagnetic clutch becomes engaged. Therefore, if the motor is driven under this condition, its drive force is transmitted to the opening/closing mechanism of the vehicle door, via the worm gear, the worm wheel, the plate spring member, the armature and the rotor. Hence, automatic opening/closing operation of the vehicle door becomes possible.
There is also known an opening/closing apparatus for a vehicle door having an electromagnetic clutch that uses a wave washer (a resilient member) between the worm wheel and the armature, instead of the plate spring member (see, e.g. Patent Document 2).
With the electromagnetic clutch used in the vehicle door opening/closing apparatus disclosed in Patent Document 2, a retaining portion of the armature is engaged with a cutout formed in the worm wheel. In the case of this electromagnetic clutch, the armature is movable relative to the worm wheel in a rotational axis direction. When the electromagnetic clutch is under the non-powered state, in order to prevent noise generation due to vibration, the wave washer interposed between the worm wheel and the armature presses the armature against the rotor. When the electromagnetic clutch enters the powered state, due to the magnetic force, the force pulls the armature toward the rotor, so the armature comes into firm contact with the rotor. That is to say, in the case of the vehicle door driving apparatus disclosed in Patent Document 2, the armature is always in contact with the rotor, whether the electromagnetic clutch is under the powered state or the non-powered state. In this, however, when the electromagnetic clutch is under the non-powered state, the contact force from the armature against the rotor is not so strong. So, when the opening/closing operation of the vehicle door is effected manually, this will cause the armature to slide and rotate relative to the rotor.
Further, in the case of such electromagnetic clutch disclosed in Patent Document 1 or the like, power supply to the electromagnetic coil is done conventionally by a power supply unit connected to a power source such as a battery via a lead wire (see e.g. Patent Document 3).
The power supply unit used in Patent Document 3 has an arrangement that a brush holder having a brush is rotatably mounted to a ring holder having a slip spring. And, power connection to this power supply unit is done by connecting a tab formed at a part of the slip spring to the lead wire extended from a battery disposed outside.
As another power supply unit, there is known a power supply unit configured to supply power to the electromagnetic clutch for a vehicle door opening/closing device with the electromagnetic clutch being fixed inside the worm wheel (see e.g. Patent Document 4).
With the power supply unit used in the vehicle door opening/closing apparatus disclosed in Patent Document 4, for the power supply, in the electromagnetic clutch in which a coil bobbin with an electromagnetic coil wound thereabout is incorporated within the worm wheel, a contact plate connected to the power source is connected, through a through hole defined in the worm wheel, to a connecting terminal of the coil bobbin. Further as shown in FIG. 3 or FIG. 5 of this document, the power supply unit has an arrangement of a slip ring being disposed immediately adjacent the worm wheel.
Incidentally, in the manufacture of an electromagnetic clutch for use in a vehicle door opening/closing apparatus or the like, there is a need for facilitating its assembly through reduction in the number of constituting parts and/or manufacturing steps, for the sake of desirable weight reduction and cost reduction.
In the above respect, with the electromagnetic clutch disclosed in Patent Document 1, this requires mutual fixing operations of the worm wheel, the plate spring and the armature by caulking, screw/bolt fastening, etc. Hence, this requires a great number of caulking pins, screws, etc. And, its assembly requires a tool(s). Moreover, in correspondence with the use of caulking pins, screws, etc., the number of parts constituting the electromagnetic clutch and the number of its manufacturing steps too will increase. For these reasons, the electromagnetic clutch disclosed in Patent Document 1 requires significant time and labor for its manufacture and high manufacture costs also.
In the case of the electromagnetic clutch for use in a vehicle door opening/closing apparatus disclosed in Patent Document 2, the worm wheel and the armature are engaged via the wave washer interposed therebetween. Therefore, unlike the electromagnetic clutch of Patent Document 1, this clutch does not require such parts as caulking pins, screws or the like for its assembly. However, since this electromagnetic clutch uses the simple fixing arrangement relying on the engagement of the retaining portion of the armature in the cutout defined in the worm wheel, there is formed a significant amount of looseness (play amount) between the worm wheel and the armature. For this reason, transmission delay tends to occur in the transmission of drive force between the worm wheel and the armature, which in turn may lead to a trouble at the time of opening/closing of the vehicle door, depending on the control condition. For instance, in detection of a foreign object jam, this detection takes a long time.
Further, with this electromagnetic clutch, the armature is constantly in contact with the rotor regardless of the powered/non-powered state of the electromagnetic clutch. Hence, when the vehicle door is opened/closed manually, a noise tends to be generated due to friction between the armature and the rotor. This is another drawback of the above electromagnetic clutch.
Further, in the case of the power supply unit disclosed in Patent Document 3, the lead wire extended from the external battery is connected to the power supply unit. Therefore, this construction requires a space for laying out the lead wire. And, this laying-out operation of the lead wire needs to be taken into consideration when the connection is made. For these reasons, the assembly of the electromagnetic clutch tends to be complicated and requiring greater numbers of parts and manufacturing steps. As a result, the final product tends to occupy a large space for its mounting and higher manufacture costs as well.
In the case also of the power supply unit used in the vehicle door opening/closing apparatus disclosed in Patent Document 4, as understood from its FIG. 5, a lead wire from an external battery is connected to the power supply unit. For this reason, this suffers the same drawback as the power supply unit disclosed in Patent Document 2.
Moreover, with this power supply unit, the slip ring is disposed immediately adjacent the worm wheel. Therefore, a foreign object or material such as an amount of grease applied to the worm wheel tends to adhere to the slip ring, thus tending to invite a conduction trouble such as short circuiting.
The present invention has been made in view of the above-described states of the art and its one object is to provide an electromagnetic clutch which requires fewer numbers of parts and manufacturing steps and which also can be assembled easily.
A further object of the present invention is to prevent delay in the transmission of drive force between the worm wheel and the armature and to realize superior quietness at the time of vehicle door operation.    Patent Document 1: Japanese Utility Model Application “Kokai” No. 5-71463    Patent Document 2: Japanese Patent Application “Kokai” No. 2004-324171    Patent Document 3: Japanese Patent Application “Kokai” No. 2007-135367    Patent Document 4: Japanese Patent Application “Kokai” No. 2005-248583